Adsorption of malachite green and methyl orange onto waste tyre activated carbon using batch and fixed-bed techniques: isotherm and kinetics modeling

Abstract

The adsorption of malachite green (MG) and methyl orange (MO) from aqueous solution by waste tyre-derived activated carbon (WTAC) using in batch and fixed-bed column methods was studied. Freundlich model with high correlation coefficient (0.99) described the adsorption data more suitably than other models, indicating multi-layer adsorption of dyes onto heterogeneous WTAC surface. The maximum Langmuir monolayer adsorption capacity was 29.23 g/kg for MG and 13.56 g/kg for MO. The adsorption obeyed pseudo-second order model, following both film-diffusion as well as intra-particle diffusion mechanisms. The thermodynamic parameters indicated spontaneous and endothermic adsorption. Fixed-bed column studies at varying flow rates between 3–5 mL/min for MG and 2–3 mL/min for MO, initial dye concentration (40–50 mg/L), and bed heights (1–2 cm) indicated that breakthrough time and exhaustion time increased with decreasing flow rate, increasing bed height and decreasing initial dyes concentration. The experimental data fitted well with Thomas and Adams–Bohart models with maximum Thomas model adsorption capacity of 71.71 g/kg for MG and 6.86 g/kg for MO. Thus, WTAC proved a promising adsorbent for the removal of MG and MO from aqueous solution.